How Much Does a Wrap Around Extension Cost?

Around £2,600 to £3,500 per square metre for the shell and a standard finish, so a 32 square metre wrap around commonly lands between £83,000 and £112,000 before VAT, fees and the exclusions below. That is the highest rate of any single storey extension type.

The reason has almost nothing to do with the quality of the building and everything to do with the shape. An L costs more per square metre than a rectangle of the same area, and once you see why, the rest of the number explains itself.

An L has more edge than a box

Cost follows perimeter, junctions and roof edges. Floor area is what you get, not what you pay for.

Take 32 square metres. As a plain rectangle across the back of a house, that is a short run of foundation, four corners, one roof plane and one junction with the existing wall. As a wrap around, the same 32 square metres has a longer trench, an extra external corner, an internal corner where the two legs meet, at least two roof planes with a valley or a step between them, and a much longer run of abutment against the original house.

Every one of those is where money and risk sit. Cavity trays, lead work, falls and outlets, damp proof course junctions, and the making good where new brickwork meets old on two elevations instead of one. Same floor, considerably more building.

The side leg makes it worse, because it is usually narrow. A two metre wide side return has almost as much wall per square metre of floor as it does floor, so the fixed costs land on very little area. That is the same effect that makes a side return on its own price above a rear extension, and a wrap around carries it on one leg while carrying rear extension economics on the other.

The corner needs its own structure

Where the two legs meet the old house, the building runs out of walls to sit on.

A wrap around normally removes the rear wall and the side wall of the original house, which leaves a corner with nothing under it. The answer is a steel frame rather than a single beam: two beams meeting over a post, the post on its own pad foundation, and the loads from both directions brought down through it. That frame is designed, fabricated, craned or carried in, and installed under temporary support on two elevations at once.

It is a genuinely different job from dropping one beam into a rear wall, and it is the single biggest structural difference between this and a plain single storey extension, and it is priced as its own item rather than inside the square metre rate.

The drains are almost always in the way

The side return is where the original drainage runs, and a wrap around builds on top of it.

On Victorian and interwar stock the soil stack, the gully and frequently an inspection chamber sit in the passage between the house and the boundary. That is the exact strip a wrap around occupies. Expect to divert a run, rebuild or replace a chamber with a suitable cover, and in many cases apply for a build over agreement because the sewer is shared and therefore the water company’s.

That brings an application fee and often a camera survey with it. None of it is a reason to avoid the job. It is a reason to have the drainage surveyed before the price is agreed rather than after the ground is open, because a chamber found at the wrong moment is a variation and a delay at the same time. How build over works is set out separately.

Two boundaries means two neighbours

On this job the party wall cost is close to certain rather than possible.

A rear extension on a semi engages one neighbour. A wrap around on a terrace commonly engages both sides and sometimes the property behind, because the side leg is built up to or against a boundary and the excavation runs alongside somebody else’s footings. Each adjoining owner is a separate matter with its own award and its own fees, and the building owner normally pays for every surveyor involved.

Three sets of fees is three sets, not one split three ways. What drives that figure, and how much of it you can influence by agreeing a single surveyor, is worth reading before the notices go out rather than after.

The access is the thing you are building on

On most extensions the side passage is how materials get to the back garden. On a wrap around, that passage is the site. Once the trench is open there is no route through, so muck goes out and blocks come in through the house or over the top, and the sequencing has to be planned rather than improvised.

This is the cost that survives every attempt to value engineer it, because it is labour and programme rather than specification.

What the range excludes

VAT, kitchen units and appliances, flooring and decoration, professional fees for drawings and structural calculations, planning and Building Control fees, party wall surveyor fees, build over application fees, service diversions and meter relocations, and anything genuinely unforeseeable once the ground is open. The complete list, with what does sit inside the rate, is on the costs page.

Planning is more likely to be needed here than on a plain rear extension, because the side leg has its own set of conditions to satisfy and the two legs have to satisfy them at the same time. It is nearly always the side leg that decides it, so check that one first.

Why it is still often the right number

A wrap around buys the one thing a rear extension cannot: a room that is wide as well as deep, on a plot that is narrow. On a terrace or a tight semi it is frequently the only way to get a kitchen, a dining area and a run of glazing into the same space without a corridor of a room.

It also does the work once. Building the rear leg now and the side return in five years costs more than doing both together, because the frame, the roof, the drainage and the party wall process all happen twice.

Turning the range into a figure

Floor area across both legs, the ground conditions, the drainage layout, the spans at the corner, the glazing, and how many neighbours are notified. With those, a quotation prices the job as it actually is. How a wrap around is designed and built covers the rest.

These figures are indicative for the Colchester area at the review date below and move with materials and labour. Use them to test a quotation rather than in place of one.

Last reviewed August 2026.